Small improvoments to specs of Hash.[]

* Remove all validations inside a block that should raise, this code
  should never be executed.
* Update the spec with `[:nil]`, to use `[nil]` instead. The old code
  tested the exact same thing as `[:a]` above it.

Author: herwinw

core/hash/constructor_spec.rb

@@ -44,22 +44,20 @@
 
   it "raises for elements that are not arrays" do
     -> {
-      Hash[[:a]].should == {}
+      Hash[[:a]]
     }.should raise_error(ArgumentError)
     -> {
-      Hash[[:nil]].should == {}
+      Hash[[nil]]
     }.should raise_error(ArgumentError)
   end
 
   it "raises an ArgumentError for arrays of more than 2 elements" do
-    ->{ Hash[[[:a, :b, :c]]].should == {} }.should raise_error(ArgumentError)
+    ->{ Hash[[[:a, :b, :c]]] }.should raise_error(ArgumentError)
   end
 
   it "raises an ArgumentError when passed a list of value-invalid-pairs in an array" do
     -> {
-      -> {
-        Hash[[[:a, 1], [:b], 42, [:d, 2], [:e, 2, 3], []]]
-      }.should complain(/ignoring wrong elements/)
+      Hash[[[:a, 1], [:b], 42, [:d, 2], [:e, 2, 3], []]]
     }.should raise_error(ArgumentError)
   end